Different chips are generally compared at similar power levels, ime. If you ran 400 watts through an M1 Ultra and somehow avoid instantly vaporizing the chip in the process, I'm sure it wouldn't be far behind the 3090.
Ok but that doesn't matter if you can't actually run 400 watts through an M1 Ultra. If you wanna compare how efficient a chip is, sure, that's a great way to test. But you can't make the claim that your chip is as good as a 3090 if the end user is never going to see the performance of an actual 3090
